1. Field of the Invention
The present invention relates to a gas sensor to be used for detecting an exhaust gas concentration of an internal combustion engine or the like to determine the air/fuel ratio of the exhaust gas and, more particularly, to a structure for extracting the electric signals of the sensor.
2. Description of the Related Art
The gas sensor is used to detect the exhaust gas concentration of an internal combustion engine or the like thereby to determine the air/fuel ratio of the exhaust gas so that the combustion of the internal combustion engine may be optimized.
In this gas sensor, a ceramic element molded into an elongate plate shape is accommodated in a cylindrical housing to be attached to the exhaust gas pipe. This ceramic element has its detecting unit exposed to the exhaust gas so that it is subjected at that portion to an electrochemical reaction by the exhaust gas components. The detecting unit is equipped with electrodes, through which the electric signals established by that reaction are extracted to the outside to detect the gas concentration.
In one method for extracting those signals, fixtures for contacting terminals are directly applied downward to the leading contacts which are disposed at the end portion of an elongated base member and conduct with electrodes (as disclosed in Japanese Utility Model Application Laid-Open (KOKAI) No. Sho. 60-150449).
As a second method, on the other hand, there is proposed a method in which a plurality of elongated sheets including the base member are laminated and are recessed at one end with recesses for preventing the contacting terminal fixtures from coming out, so that the electric signals may be reliably extracted from the base member (as disclosed in Japanese Patent Application Laid-Open (KOKAI) No. Hei. 3-235049).
In a third method, as shown in FIGS. 21 and 22, contact plates 971 attached to lead wires 97 are thrust through insulating members 973 onto electric terminal portions 911 by the actions of leaf springs 974.
According to this method, the leaf springs 974, the insulating members 973 and the contact plates 971 are sequentially arranged between a cover 950 and an oxygen detecting element, and the cover 950 is thrust from a broken-line position to a solid-line position, as shown. Moreover, the contact plates 971 are thrust onto the electric terminal portions 911 of the oxygen detecting element 91 by the elastic repulsions of the leaf springs 974.
According to the aforementioned first method, however, the base member has its end portion exposed to the thrust of the contacting terminal fixtures so that it is liable to be damaged with a crack or the like by the bending force to have an insufficient strength. The adjoining contacting terminal fixtures are liable to contact and accordingly to short. In case, moreover, a number of contacts are to be provided, they cannot be given a sufficient area and thereby effect an imperfect contact between the contacting terminal contacts and the contacting terminal fixtures.
According to the third method, on the other hand, a transverse load (i.e., a load perpendicular to the axis) is applied at assembling time or the like to the oxygen detecting element 91 to raise a problem that the oxygen detecting element 91 is liable to be broken.